converting float to string without using library function like sprintf (naive approach , may lead to anomalies)

ftos.c

#include <stdio.h>
#include <math.h>

#define precision 6  //precision for decimal digits


int main(int argc, char const *argv[])
{
        
	float f,ff;
	scanf("%f",&f);
	ff = f;
	char str[30];
	int a,b,c,k,l=0,m,i=0,j;
	
	// check for negetive float
	if(f<0.0)
	{
		
		str[i++]='-';
		f*=-1;
	}
	
	a=f;	// extracting whole number
	f-=a;	// extracting decimal part
	k = precision;
	
	// number of digits in whole number
	while(k>-1)
	{
		l = pow(10,k);
		m = a/l;
		if(m>0)
		{
			break;
		}
	k--;
	}

	// number of digits in whole number are k+1
	
	/*
	extracting most significant digit i.e. right most digit , and concatenating to string
	obtained as quotient by dividing number by 10^k where k = (number of digit -1)
	*/
	
	for(l=k+1;l>0;l--)
	{
		b = pow(10,l-1);
		c = a/b;
		str[i++]=c+48;
		a%=b;
	}
	str[i++] = '.';
	
	/* extracting decimal digits till precision */

	for(l=0;l<precision;l++)
	{
		f*=10.0;
		b = f;
		str[i++]=b+48;
		f-=b;
	}

	str[i]='\0';

	printf("\n orignal printf %f\n",ff);
	printf("\n float string %s\n",str);


	return 0;
}

256.6006

orignal printf 256.600586

float string 258.600585

Can we make it print like snprintf(.,.,"%*.*g", 0,-1, f) ?
orignal printf 1.030000
float string 1.029999

It is not working for precision=1 and 0 I edited it and it is working fine.

static void float_to_string(float f,char *str, u8 precision)
{
float ff;
//char str[30];
int a,b,c,k,l=0,m,i=0,j;
//scanf("%f",&f);
ff = f;

// check for negetive float
if(f<0.0)
{
	
	str[i++]='-';
	f*=-1;
}

a=f;	// extracting whole number
f-=a;	// extracting decimal part
k = 0;

// number of digits in whole number
while(1)
{
	l = pow(10,k);
	m = a/l;
	if(m==0)
	{
		break;
	}
k++;
}

k--;
// number of digits in whole number are k+1

/*
extracting most significant digit i.e. right most digit , and concatenating to string
obtained as quotient by dividing number by 10^k where k = (number of digit -1)
*/

for(l=k+1;l>0;l--)
{
	b = pow(10,l-1);
	c = a/b;
	str[i++]=c+48;
	a%=b;
}
if(precision != 0)
		str[i++] = '.';

/* extracting decimal digits till precision */

for(l=0;l<precision;l++)
{
	f*=10.0;
	b = f;
	str[i++]=b+48;
	f-=b;
}

str[i]='\0';

//printf("\n orignal printf %f\n",ff);
//printf("\n float string %s\n",str);

}

Stumbled upon a corner case which caused my program to crash when trying to convert a float without any assigned decimals.

Does work:

float f = 12345.6;

Does not work:

float f = 12345.0;

This is caused by multiplying with 0 inside this for loop (when I >= 1):

    /* extracting decimal digits till precision */

    for (l = 0; l < PERCISION; l++)
    {
        f *= 10.0;
        b = f;
        str[i++] = b + 48;
        f -= b;
    }

To fix this, just exit the for loop whenever f == 0 :

    /* extracting decimal digits till precision */

    for (l = 0; l < PERCISION; l++)
    {
        f *= 10.0;
        b = f;
        str[i++] = b + 48;
        f -= b;

        if (f == 0)
        {
            break;
        }
    }